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authorMark Fasheh <mfasheh@suse.de>2015-05-19 12:49:50 -0700
committerChris Mason <clm@fb.com>2015-05-19 18:04:17 -0700
commit2c2ed5aa0154c0be67f98c970de6b5587dbc045a (patch)
tree93a9be4a974851d8a164b621711f3721d5966d5d /fs
parent062c19e9dd692b8a78e3532f71c290520a2ab437 (diff)
downloadkernel-2c2ed5aa0154c0be67f98c970de6b5587dbc045a.tar.gz
btrfs: clear 'ret' in btrfs_check_shared() loop
btrfs_check_shared() is leaking a return value of '1' from find_parent_nodes(). As a result, callers (in this case, extent_fiemap()) are told extents are shared when they are not. This in turn broke fiemap on btrfs for kernels v3.18 and up. The fix is simple - we just have to clear 'ret' after we are done processing the results of find_parent_nodes(). It wasn't clear to me at first what was happening with return values in btrfs_check_shared() and find_parent_nodes() - thanks to Josef for the help on irc. I added documentation to both functions to make things more clear for the next hacker who might come across them. If we could queue this up for -stable too that would be great. Signed-off-by: Mark Fasheh <mfasheh@suse.de> Reviewed-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/backref.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 9de772ee0031..614aaa1969bd 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -880,6 +880,8 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
* indirect refs to their parent bytenr.
* When roots are found, they're added to the roots list
*
+ * NOTE: This can return values > 0
+ *
* FIXME some caching might speed things up
*/
static int find_parent_nodes(struct btrfs_trans_handle *trans,
@@ -1198,6 +1200,19 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
return ret;
}
+/**
+ * btrfs_check_shared - tell us whether an extent is shared
+ *
+ * @trans: optional trans handle
+ *
+ * btrfs_check_shared uses the backref walking code but will short
+ * circuit as soon as it finds a root or inode that doesn't match the
+ * one passed in. This provides a significant performance benefit for
+ * callers (such as fiemap) which want to know whether the extent is
+ * shared but do not need a ref count.
+ *
+ * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
+ */
int btrfs_check_shared(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info, u64 root_objectid,
u64 inum, u64 bytenr)
@@ -1226,11 +1241,13 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
roots, NULL, root_objectid, inum);
if (ret == BACKREF_FOUND_SHARED) {
+ /* this is the only condition under which we return 1 */
ret = 1;
break;
}
if (ret < 0 && ret != -ENOENT)
break;
+ ret = 0;
node = ulist_next(tmp, &uiter);
if (!node)
break;